ST. LOUIS >> A federal investigation into the police killing of an unarmed, black 18-year-old in Ferguson, Missouri, lays bare what officials contend are racist, profit-driven law enforcement practices in the small St. Louis suburb.

While the Department of Justice cleared Officer Darren Wilson of federal civil rights charges in the August death of Michael Brown, it also called for sweeping changes in a city where officers trade racist emails, issue tickets mostly to black drivers that generate millions of dollars in revenue, and routinely use what investigators called excessive force on people stopped for minor or non-existent offenses.

Attorney General Eric Holder said Wednesday that the department “found a community that was deeply polarized; a community where deep distrust and hostility often characterized interactions between police and area residents.”

Ferguson Mayor James Knowles III said steps are already being taken to correct problems.

“We must do better not only as a city, but as a state and a country,” Knowles said.

The shooting of Brown sparked a national dialogue on race and law enforcement. Separate federal investigations into the shooting and the police department began soon after Brown was killed.

In pairing the announcements on the investigations’ results, the Obama administration sought to offset community disappointment over the conclusion that the shooting was legally justified with a message of hope for Ferguson’s majority-black citizens.

Officials announced 26 recommendations, including training officers in how to de-escalate confrontations and banning the use of ticketing and arrest quotas.

Wilson was cleared in November by a state grand jury, a decision that set off protests, looting and fires. The federal report concurred that there was no evidence to disprove Wilson’s testimony that he feared for his safety. Nor were there reliable witness accounts to establish that Brown had his hands up in surrender when he was shot, Justice Department lawyers said.

An attorney for Wilson, Neil Bruntrager, described the officer as “very happy” with the outcome.

Ben Crump, the attorney for Brown’s parents, said the family was “extremely disappointed. This underscores the need for change and reform when there is continued use of excessive deadly force on people of color by police officers.”

About 30 protesters braved sub-freezing weather Wednesday night to gather outside Ferguson’s police station. Four of them who ignored police warnings to clear the road were handcuffed and taken into custody. By 10:30 p.m., most of the protesters had dispersed.

While the federal government declined to prosecute Wilson, it raised grave concerns about the operation of Ferguson’s police department and municipal court. Though about two-thirds of the city’s 21,000 residents are black, only four of 54 commissioned officers are African-American.

That lack of diversity undermines community trust, the Justice Department’s report said. It also found Ferguson relies heavily on fines for petty offenses, such as jaywalking, to raise revenue.

Holder said the city collected more than $1.3 million in fines and court fees in 2010, but $3 million more is projected for the current fiscal year.

“Our review of the evidence, and our conversations with police officers, have shown that significant pressure is brought to bear on law enforcement personnel to deliver on these revenue increases,” Holder said.

He cited a 2007 case where a woman received two parking tickets costing $152. Because of court fees and other expenses, she has paid $550 so far, spent six days in jail, and still owes $541.

Another woman, Tiffany Tunstall, 34, told The Associated Press that she received “threatening” letters for nearly two years after paying off traffic tickets through an installment plan.

“I didn’t want to have anything to do with the city I was raised in,” she said. “I felt disrespected.”

Activist John Gaskin III, a member of the national NAACP board of directors, said lines outside of municipal court are often long.

Federal investigators found many other examples of discrimination. A lawful protest was broken up with a police warning of “everybody here’s going to jail.” And a black man sitting in a car with tinted windows was accused without cause of being a pedophile by an officer who pointed a gun at his head.

Between 2012 and 2014, black drivers were more than twice as likely as others to be searched during routine traffic stops, but 26 percent less likely to be carrying contraband.

The report also included seven racially tinged emails that did not result in punishment. The writer of one 2008 email stated that President Barack Obama would not be in office for long because “what black man holds a steady job for four years.”

Knowles said three employees were responsible for those emails. One was fired Wednesday, and the other two are on administrative leave pending an investigation, he said. He did not take questions, and Police Chief Tom Jackson was not at the news conference where the mayor spoke.

The report’s recommendations, if accepted by city officials, could lead to an overhaul of basic practices by police officers and court officials. Those include improving officer supervision, better recruiting, hiring and promotion and new mechanisms for responding to misconduct complaints.

Federal officials described Ferguson leaders as cooperative and open to change and said there were already signs of improvement. The city, for example, no longer issues failure-to-appear warrants, has eliminated a fee for towing cars and rescinded warrants for nearly 600 defendants.

Under Holder, the Justice Department has investigated roughly 20 police departments over alleged civil rights violations. Some have led to the appointment of independent monitors and have been resolved with agreements in which police commit to major changes.

“It’s quite evident that change is coming down the pike. This is encouraging,” Gaskin said. “It’s so unfortunate that Michael Brown had to be killed. But in spite of that, I feel justice is coming.”

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Associated Press writers Jim Suhr in St. Louis and Alan Scher Zagier in Ferguson contributed to this report.